Referring to FIG. 1, a known stack 11 of fuel cells 13 applying gaseous reactants to a proton exchange membrane electrolyte, in a unitized electrode assembly 15, may be of the type employing porous, hydrophilic separator plates, which typically have gaseous reactant grooves on one surface of each substrate and grooves 16 for coolant, typically water, on the opposite surface. The cathode water transport plate 18 of one fuel cell flows oxidant in its reactant gas grooves 19 and the anode water transport plate 22 of the adjacent fuel cell, with which it is in contact, flows fuel in its reactant gas grooves 23. The fuel and oxidant are isolated from each other by water in the pores of the water transport plates, the capillary forces of which require a certain pressure for bubbles to pass through the water, which is called bubble pressure.
As the fuel cell stack is assembled, dimensional tolerances and positioning tolerances of the water transport plates, relative to each other and to the unitized electrode assembly, results in substrate edge misalignment which has been labeled a “skyline”, as is illustrated by the differing heights of WTPs 18, 22 and the unitized electrode assemblies 15. Because of that, in order to provide a relatively smooth area for sealing the fuel cell edges to a surface of an external reactant gas manifold, such as the oxidant manifold 27, an elastomer filler, such as silicone rubber 29 is applied to the uneven edge surfaces of the fuel cells. This provides a sufficiently smooth bed for a rubber gasket 30 between the edge of the manifold 27 and the silicone 29, as described in U.S. Pat. Nos. 6,660,422 and 7,122,384, both incorporated herein by reference. In some instances, a thin rigid strip, which may be dielectric, is provided between the rubber gasket and the silicone 29.
It has been found that, in the area where the manifold 27 is sealed to fuel cells 13, leakage of reactant gas from the channels 19, 23 into the coolant in the channels 16 occurs to such an extent that the coolant pump cannot function. This happens in all fuel cell stacks, limiting the life of the stacks. It has also been found that replacing the external portions of the seal, such as a fresh layer of silicone and/or a new rubber gasket 30 are not effective in most cases. Typically, the stack has to be reassembled. After disassembly, the effected cell is useless and the material is, at best, recycled.